Creating Database Tables © Abdou Illia MIS Spring /21/2015

2 Objectives  Use structured query language (SQL) commands to create, modify, and drop database tables  Explain Oracle 10g user schemas  Define Oracle 10g database tables  Create database tables using SQL*Plus  View information about your database tables using Oracle 10g data dictionary views

3 Introduction to SQL  Structured query language (SQL) –Standard query language for relational databases –Consists of about 30 commands –Enables users to create database objects and manipulate and view data –SQL-99, SQL-2003, and SQL-2008 Most recent versions Most vendors do not fully comply with SQL-2008 (but comply with SQL-92, SQL-99) –Basic categories for SQL commands Data definition language (DDL) Data manipulation language (DML) CH2:42-58

4 Personal DBMS  With personal DBMS … –You are usually the only user –You start the database application –You create a new database –The DBMS saves the database file in your workstation’s file system –You create database objects (tables, etc.)  Examples: –MS Access –Oracle Personal edition. But this DBMS derives most of its features from the Oracle C/S version CH2:42-58

5 Oracle 10g Enterprise edition  A Client/server DBMS  User account –Created for each user –Identified using unique username and password  User schema –Area of database belonging to user  Database objects –Example: tables, forms, reports, … –Also called schema objects –Objects created by user reside in their user schema CH2:42-58

6 Defining Oracle Database Tables  Tables –Primary data objects in relational database –When you create a new table, you must specify… Table name ● Each field (i.e. column) name Each field data type/size ● You may specify constraints  Constraints –Restrictions on data values that column can store  Oracle naming standard –Rules established by Oracle corp. for naming objects –One to 30 characters long –Contain letters, numbers, and special symbols $, _, and # –Begin with character –Example: S_ID, f_id, PRICE, PRICE$, Not #ITEM. CH2:42-58

7 Defining Oracle Database Tables (cont.)  CREATE TABLE SQL syntax CREATE TABLE tablename (columnname1 data_type, columnname2 data_type, …);  Example: CREATE TABLE student (s_id CHAR(5), s_first VARCHAR2(20));  Basic data types Character ● Number ● Date/time ● Large object CH2:42-58

8 Character Data Types  VARCHAR2 –Variable-length character data (up to 4000 characters) –Syntax: columnname VARCHAR2(maximum_size) –If user enters data value less than maximum_size, DBMS only stores actual character values  CHAR –Fixed-length character data (default = 2000) –Syntax: columnname CHAR(maximum_size) –If user enters data value less than maximum_size, DBMS adds trailing blank spaces to the end of entry  Oracle stores CHAR and VARCHAR2 data using the ASCII coding Q: s_last CHAR(20) was used to define the data type for s_last in the Student table. How many characters will Oracle save to the disk if the user enters illia as the student’s last name?

9 Character Data Types (continued)  Unicode coding –Standardized technique that provides way to encode data in diverse languages  NVARCHAR2 –Counterpart of VARCHAR2 –Uses Unicode coding  NCHAR –Counterpart of CHAR –Uses Unicode encoding CH2:42-58

10 Number Data Types  NUMBER –Used for all numeric data –Syntax columnname NUMBER [([precision,] [scale])]  Example: –s_balance NUMBER (5,2) –s_gpa NUMBER (3,2) # of digits both to left and right of decimal point # of digits on the right side of decimal point CH2:42-58

11 Number Data subtypes  Integer number syntax –columnname NUMBER(precision)  Fixed-point number –Contains specific number of decimal places –Column declaration specifies both precision and scale –Example: price NUMBER(5,2)  Floating-point number –Contains variable number of decimal places –Decimal point may appear anywhere (.005, 2.34, etc.) –Syntax: columnname NUMBER –Example: s_gpa NUMBER Just the precision. No scale specified No precision, no scale CH2:42-58

12 Date And Time Data Types  Datetime data subtypes –Store actual date and time values –DATE –TIMESTAMP  Interval data subtypes –Store elapsed time interval between two datetime values –INTERVAL YEAR TO MONTH –INTERVAL DAY TO SECOND CH2:42-58

13 Date And Time Data Types (continued)  DATE –Stores dates from Dec 31, 4712 BC to Dec 31, AD 4712 –Default date format: DD-MON-YY –Default time format: HH:MI:SS AM –Syntax: columnname DATE  TIMESTAMP –Stores date values similar to DATE data type –Also stores fractional seconds –Syntax: columnname TIMESTAMP (fractional_seconds_precision) –Example : shipment_date TIMESTAMP(2) If omitted, default is 6 decimal place

14 Date And Time Data Types (continued)  INTERVAL YEAR TO MONTH –Stores time interval expressed in years and months using the following syntax: +|– elapsed_years-elapsed_months –Example: specifies 2 years and 11 months –Example: time_enrolled INTERVAL YEAR TO MONTH CH2:42-58

15 Date And Time Data Types (continued)  INTERVAL DAY TO SECOND –Stores time interval expressed in days, hours, minutes, and seconds using the following syntax: Columnname INTERVAL DAY [(leading_precision)] TO SECOND [(fractional_seconds_precision)] Max allowed number of digits used to express the elapsed days Max allowed number of digits used to express the elapsed seconds CH2:42-58

16 Large Object (LOB) Data Types  Store binary data such as: –Digitized sounds or images –References to binary files from word processor or spreadsheet  General syntax –columnname Lob_data_type

17 Constraints  Table constraint –Restricts data value with respect to all other values in table like primary key must be unique, not NULL.  Column constraint –Limits value that can be placed in specific column –Irrespective of values that exist in other table rows  Types of constraints: –Integrity constraints –Value constraints CH2:42-58

CREATE TABLE location (loc_id NUMBER(6) CONSTRAINT location_loc_id_pk PRIMARY KEY), Room VARCHAR2(6); 18 Constraints (cont.)  Constraint naming convention –tablename_columnname_constraintid  Constraint definitions should be placed either: –At end of CREATE TABLE command after table columns declared –Within each column definition  Example: CREATE TABLE location (loc_id NUMBER(6), Room VARCHAR2(6), CONSTRAINT location_loc_id_pk PRIMARY KEY (loc_id); Q: Is there any syntax error (or something missing in the above CREATE TABLE statements?

19 Integrity Constraints  Primary key –Syntax (within table definition) CONSTRAINT constraint_name PRIMARY KEY –Syntax (at end of table definition) CONSTRAINT constraint_name PRIMARY KEY (columnname) CREATE TABLE location (loc_id NUMBER(6), Room VARCHAR2(6), CONSTRAINT location_loc_id_pk PRIMARY KEY (loc_id)); CREATE TABLE location (loc_id NUMBER(6) CONSTRAINT location_loc_id_pk PRIMARY KEY), Room VARCHAR2(6)); CH2:42-58

20 Integrity Constraints (continued)  Foreign key –Column constraint –Specifies that value user inserts in column must exist as primary key in referenced table –Syntax (placed at end of table definition) CONSTRAINT constraint_name FOREIGN KEY (columnname) REFERENCES primary_key_tablename (primary_key_columnname) –Example of foreign key defined in the Faculty table: CONSTRAINT faculty_loc_id_fk FOREIGN KEY (loc_id) REFERENCES location (loc_id) CH2:42-58

21 Integrity Constraints (continued)  Foreign key (continued) –Syntax (placed within table definition) CONSTRAINT constraint_name REFERENCES primary_key_tablename (primary_key_columnname) –Example: loc_id NUMBER(6) CONSTRAINT faculty_loc_id_fk REFERENCES location (loc_id) CH2:42-58

22 Integrity Constraints (continued)  Composite key –Syntax CONSTRAINT constraint_name PRIMARY KEY (columnname1, columnname2 …) –Example: CREATE TABLE enrollment (s_id NUMBER(5) CONSTRAINT enrollment_s_id_fk REFERENCES student(s_id), c_sec_id NUMBER(8) CONSTRAINT enrollment_c_sec_id_fk REFERENCES course_section(c_sec__id), CONSTRAINT enrollment_s_id_c_sec_id_pk PRIMARY KEY (s_id, c_sec_id)); CH2:42-58

23 Value Constraints  Value constraints –Column-level constraints –Restrict data values that users can enter –Commonly used value constraints CHECK conditions ● NOT NULL constraint DEFAULT constraint ● UNIQUE constraint CONSTRAINT student_s_class_cc CHECK ((s_class = ‘FR’) OR (s_class = ‘SO’) OR (s_class = ‘JR’) OR (s_class = ‘SR’)) CONSTRAINT course_credits_cc CHECK ((credits > 0) AND (credits < 12)) S_last VARCHAR2(30) CONSTRAINT student_s_last_nn NOT NULL s_state CHAR(2) DEFAULT ‘FL’